Keyboard anomalies with large files open

I have a large file (Jazz Harmony) open as reference and I am working on converting midi files to Musescore format. In Jazz Harmony I only do a couple goto page xxx. In the converted midi files I am entering chords via Ctrl-K.
After working for a while I type Ab for the chord & get Qb instead (I have an azerty keyboard). At that point Ctrl-W to quit does not work any more in Musescore or in other apps. After I reboot everything is fine.
Unfortunately, I cannot give a precise reproducible scenario, but what I described has happened twice already.
Seems like something is stepping on the keyboard tables.
I attach the files where it occured.
I run Windows 10 & Musescore 2.1.0 revision 871c8ce